Method and apparatus for creating pulsed magnetic field in a large volume

ABSTRACT

This disclosure concerns a method and apparatus for creating a pulsed magnetic field in a large volume wherein the pulsed magnetic field may simulate the electromagnetic pulse effects produced by a nuclear detonation. The apparatus comprises an explosive generator disposed in an electrical circuit which includes a segmental inductive loop having a plurality of individual loop segments. The individual loop segments are respectively connected in series in the electrical circuit with the explosive generator and in parallel with respect to each other. The explosive generator includes an explosive charge mounted in a cylindrical armature which is surrounded by helical inductor coil. Upon discharging a pulse of electrical current through the inductor coil and detonating the explosive charge at one end of the armature, the armature is expanded so as to progressively contact the surrounding inductor coil along the length thereof. Thus, the electrical circuit is progressively short circuited, and the trapped magnetic flux is compressed. The trapped magnetic flux is then transferred by the explosive generator into the individual loop segments of the inductive loop with a corresponding increase in current and energy thereby establishing a pulsed magnetic field within the loop volume which is sufficiently large to simulate the electromagnetic pulse effects of a nuclear detonation.

FIP8502 Ullllefl DIHIES ratent [72] Inventor David B. Cummings Alamo, Calif. [21] Appl. No. 445,495 [22] Filed Apr. 5, 1965 [45] Patented Feb. 16, 1971 [73] Assignee By mesne assignments, to

Aerojet General Corp. El Monte, Calif. Continuation-impart of application Ser. No. 390,408, Aug. 18, 1964, now abandoned.

[54] METHOD AND APPARATUS FOR CREATING PULSED MAGNETIC FIELD IN A LARGE VOLUME 6 Claims, 3 Drawing Figs.

[52] U.S.Cl 310/10; 307/106; 336/180 [51] Int. Cl H02k [50] Field ofSearch 328/1; 336/1 80186, 223, 225, 229; 310/10, 1 l; 307/ l 06 [56] References Cited UNITED STATES PATENTS 526,487 9/1894 Herberts 336/186X 2,151,035 3/1939 Kennedy 336/233X 2,181,899 12/1939 Kennedy 336/186X 3,225,227 12/1965 Biehl 310/11 Primary Examiner.l. D. Miller Assistant Examiner-D. F. Duggan At!0rneys Edward O. Ansell, D. Gordon Angus and William E. Hiller ABSTRACT: This disclosure concerns a method and apparatus for creating a pulsed magnetic field in a large volume wherein the pulsed magnetic field may simulate the electromagnetic pulse effects produced by a nuclear detonation. The apparatus comprises an explosive generator disposed in an electrical circuit which includes a segmental inductive loop having a plurality of individual loop segments. The individual loop segments are respectively connected in series in the electrical circuit with the explosive generator and in parallel with respect to each other. The explosive generator includes an explosive charge mounted in a cylindrical armature which is surrounded by helical inductor coil. Upon discharging a pulse of electrical current through the inductor coil and detonating the explosive charge at one end of the armature, the armature is expanded so as to progressively contact the surrounding inductor coil along the length thereof. Thus, the electrical circuit is progressively short circuited, and the trapped magnetic flux is compressed. The trapped magnetic flux is then transferred by the explosive generator into the individual loop segments of the inductive loop with a corresponding increase in current and energy thereby establishing a pulsed magnetic field within the loop volume which is sufficiently large to simulate the electromagnetic pulse effects ofa nuclear detonation.

PATENTED FEB1 6 l97l I 3564.305

' INVENTOR. DAVID B. CUMMINGS 6. Wm ATTORNEY AGENT METHOD AND APPARATUS FOR CREATING PULSED MAGNETIC FIELD IN A LARGE VOLUME This is a continuation-in-part of my copending application, Ser. No. 390,409,filed Aug. I8, 1964, now abandoned.

This invention generally relates to an explosive generator system and more particularly to a novel low-inductance segmented load for coupling to an explosive generator and to a novel method of providing a pulsed magnetic field in a large volume.

An explosive generator is a device in which electrical energy provided by a small auxiliary energy source is multiplied by the direct conversion of high explosive energy to electrical energy. This conversion results from the extremely rapid deformation of the electrical circuit acted upon by the explosive. Typically, a high explosive inside a central tubular conductor, called the armature, is detonated at one end. The armature then expands in the form of a cone behind the moving detonation front. The expanding armature contacts an outer inductor such as a helix, thereby progressively short-circuiting the circuit, reducing the inductance, and compressing the trapped magnetic flux. This continues to the end of the generator when all of the trapped magnetic flux (neglecting losses) is transferred into a load with a corresponding increase in current and energy.

One potential use of an explosive generator is to drive an electrical current through a large loop or coil to create a pulsed magnetic field within a large volume. Of particular interest is the simulation of the near or induction magnetic field produced by a nuclear detonation. This primarily horizontal field, resulting from the vertical currents associated with the detonation near the earth is considered to be the principal effect of the nuclear detonation. The hazard to exposed equipment lies in the voltages and currents which this changing magnetic field induces in closed loops. If small, these pulses may couple into circuits and cause malfunction, while if large, components may be burned out thus disabling the equipment. In the absence of atmospheric nuclear testing to test directly the susceptibility of equipment to these nuclear electromagnetic pulses, it is necessary that suitable simulation testing devices be developed.

The multiplication or gain resulting from usual explosive generators has been found, however, to be limited by the ratio of the initial circuit inductance to the inductance of the load. Since the explosive generator has a low inductance, it is only useful operating into loads of still lower inductance. Large loops, on the other hand, typically have a high inductance in the range of to 10- henries, comparable to that of the highest inductance explosive generator. A range of 10- to 10- is required for useful operation of the explosive generator. Thus, the major obstacle of using an explosive generator is this manner is the high inductance of asingle large loop.

It is therefore an object of this invention to provide a novel means for and an improved method of coupling an explosive generator to an inductive load resulting in a high system gain.

Another object of this invention is to provide a novel inductive load for coupling an explosive generator.

Yet another object of this invention is to provide a novel means for providing a pulsed magnetic field in a large volume wherein an explosive generator is coupled to a segmented inductive loop resulting in a high energy gain.

In its principal aspect, the present invention comprises an inductive loop having a plurality of electrically parallel segments connected in electrical series with an explosive generator. The electrical current forced through the segmented loop by the explosive generator will establish a pulsed magnetic field within the loop volume which, if sufficiently large, will simulate the electromagnetic pulse effects of a nuclear detonation.

These and other objects, advantages, and features of the present invention will be apparent to those skilled in the art from the-following description taken together with the appended drawings, wherein:

FIG. 1 is a diagrammatic view of an electrical circuit comprising an explosive generator system in accordance with the present invention, certain components of the circuit being shown in cross section for purposes of clarity;

FIG. 2 is a transverse cross-sectional view of an explosive generator forming one of the components of the electrical circuit shown in FIG. 1 and taken along line 2-2 of FIG. I; and

FIG. 3 is a transverse cross-sectional view of a segmented inductor forming another component of the electrical circuit shown in FIG. 1 and taken along line 3-3 of FIG. 1.

The explosive generator system of FIG. 1 generally comprises an explosive generator 10 coupled in electrical series to a segmented inductive load 12. The explosive generator 10 comprises a cylindrical conductor armature 14 which is filled with a high energy explosive 16, the cylindrical armature 14 being concentrically arranged within a helical inductor 18. A detonator 20 is provided at one end of the high energy explosive 16. A small electrical energy source 22, such as a capacitor bank, and an electrical switch 24 are connected in electrical series with the detonator end of the armature l4 and inductor 18. Electrical leads 26 extend from the other end of the armature l4 and inductor 18 for series electrical connection to the load 12. It will be understood that other suitable explosive generators may be used within the spirit of this invention, such as, for example, any of the explosive generators which are disclosed in copending US. application, Ser. No. 324, 133, filed Nov. 15, 1963, now US. Pat. No. 3,356,869 issued Dec. 5, 1967.

Operation of the explosive generator 10 is initiated by closing the switch 24 which permits the capacitor 22 to discharge through'the inductor 18. The high energy explosive 16 is then ignited by means of the detonator 20, thus expanding the armature 14 in the form of a cone'behind the moving detonation front. Detonation of the explosive 16 is timed so that the leading edge of the armature 14 will contact the leading edge of the inductor 18 when the current wave from the capacitor 22 is at its maximum. This initial contact of the expanding armature 14 and the inductor l8 removes the capacitor 22 and switch 24 from the initial electrical circuit. As the expansion of the armature l4 continues, its point of contact with the helical inductor 18 travels around the inside of the helix, progressively and continuously shorting out the winding, reducing the inductance, and compressing the trapped magnetic flux. This trapped magnetic flux (neglecting losses) is transferred into the load 12 with a substantial increase in current and energy from that supplied by the capacitor 22.

To assist in understanding what is believed to be the theory of operation, the explosive generator circuit may be considered as having a resistance R and an inductance L which surrounds an initial magnetic flux 1 Since the load 12 is connected in electrical series with the explosive generator 10, its resistance, inductance and flux must be included in the circuit.

The sum of the voltages around this circuit may be written If it is assumed that neither L nor R is a constant, the following definition of inductance is invoked:

This expression may be rewritten as:

The solution of this equation is:

Again, by using eq. (2), the expression for current may be written in the following form:

= initial inwhere 1,, initial current L ductance.

From equation it can be seen that the current can be increased by reducing L(t) in a time short compared to the circuit decay time L(t)/R(t) which in general is changing during this time. Physically this is done by exploding the armature 14 with the high explosive 16. The circuit energy which is stored in the magnetic field is:

L t I t 2 The expression for current may be substituted and the equa tion rewritten in the form: f

L m/ 401M W(t)W L )e (7) where W, L l /2, It is apparent that there can be a net gain in circuit energy if deformation of the circuit is done rapidly.

As can be seen from equations (5) and (7) the upper limit of both current and energy gain for the explosive generator is the ratio of initial to final or load inductance L lL This ratio must be in the range of 10 to 10 to provide reasonable power gain after normal electrical losses have taken their toll.

The inductance of a single circular loop of wire for use as the load of an explosive generator can be approximated by:

L=p. 7' [1n 2] henries (8) where o permeability r= loop radius and a wire radius. A -m. radius loop with a conductor radius of 1 cm. would have an inductance of about 194 u henries. It is apparent that because of this large inductance an extremely large generator would be required to obtain a substantial energy multiplication.

As shown in HO. 1, however, the present invention divides the loop 12 (the load for the explosive generator 10) into a plurality of segments 28 a f. The drawing illustrates the number of segments 28 as six although more or less may be 2 Fix I- where I is total number offiux linkages and l is total current, Each segment links I /N of the total flux; therefore Saxmeut'- When all the segments are placed in parallel, the inductance a iea il le. llith ie sestee Therefore the inductance of the loop 12 has been reduced by a factorof N when compared to the single wire loop.

The inductance of the transmission lines running to each segment 28 can be made as small as desired by using the appropriate number of cables in parallel.

- If 30 drive points are used, the inductance of a 20-m. radius loop will be reduced from 194 p. henries to 0.21 p. henries. An explosive generator with an inductance of 1,000 ,1. henries using 100 lbs. of high explosive, can induce 10 M joules into the magnetic field of such a loop inductance.

Considering the parallel segment coupling method from a physical point of view, it can be seen that paralleling reduced the very high current from the generator (10 million amperes is typical of efficient generator performance) to the much smaller value'appropriate to the required magnetic field. For

example, if gauss is desired at the center of a 20-m. radius loop, then the necessary current] is given by where B is the field in webers a, permeability 4n l0" 1 319,000 a. a number much smaller than 10 a.

The stored energy in the magnetic field from E lLl where L g henries, is found to be E 10 joules. In this manner it is possible to couple an explosive generator to a large loop to provide a pulse magnetic field in a large volume. Electromagnetic pulses with component frequencies in excess of 10 kilocycles per second can be achieved to simulate the induction effects of nuclear detonations.

While a specific embodiment of the invention has been illustrated and described, it is to be understood that this embodiment is by way of example only, and that the invention is not to be construed as being limited thereto, but only by the proper scope of the appended claims.

I claim:

1. A high gain explosive generator system comprising:

a. explosive generator means for establishing a pulsed electrical current; and

b. inductive load means connected to said generator means,

said load means comprising a single inductor member divided into physically separated segments, each of said segments being connected in electrical series with said generator means but in electrical parallel with each other.

2. A high gain explosive generator system comprising:

a. explosive generator means for establishing a pulsed electrical current; and

b. inductive load means connected in series to said generator means, said load means comprising a single discontinuous inductive loop having a plurality of segments connected in electrical parallel with each other.

3. A method of simulating the electromagnetic effects of a nuclear detonation comprising:

a. enclosing a volume with a discontinuous inductive loop having a plurality of segments connected in electrical parallel; and

b. driving a pulsed electric current from an explosive generator through said loop segments to establish a pulsed magnetic field within the enclosed volume, each of said segments beingconnected in electrical series with the explosive generator.

4. A method of creating a pulsed magnetic field in a confined volume comprising:

a. discharging a pulsed electrical current through the inductor of an explosive generator comprising an explosivecontaining armature and an inductor surrounding'the armature;

. detonating the explosive contained in the armature of the explosive generator in timed relation to the discharge of the pulsed electrical current through the inductor of the explosive generator such that successive expansion of the armature due to the detonation of the explosive con tained therein causes progressive contact between the armature and the inductor of the explosive generator along the lengths thereof for compressing magnetic flux; and

c. directing the compressed magnetic flux having a substantial increase in current and energy from the pulsed electrical current through a segmented inductive loop having a plurality of individual loop segments respectively connected in series in an electrical circuit with theexplosive generator and in parallel with respect to each other.

. A high gain explosive generator system comprising:

an electrical circuit;

. explosive generator means disposed in said electrical circuit for providing compressed magnetic flux upon actuation thereof by an explosion;

c. a segmented inductive loop disposed in said electrical circuit and'havinga plurality of individual loop segments respectively connected in series in the electricalcircuit.

with said explosive generator means and in parallel with respect to each other;

d. means in said electrical circuit for discharging a pulsed electrical current through at least a portion of said explosive generator means; and

e. means operating in timed relation to the discharge of the pulsed electrical current to cause an explosion actuating said explosive generator means, whereby the compressed magnetic flux provided by the actuation of said explosive generator means is driven through said loop segments to establish a pulsed magnetic field within said segmented inductive loop.

6. A high gain explosive generator system comprising:

a. an electrical circuit;

b. an explosive generator disposed in said electrical circuit and comprising;

1. an armature containing an explosive therein; 2. inductor means surrounding said armature; and

3. detonator means in proximity to the explosive con-- tained in said armature and actuatable for detonating the explosive;

c. said armature and said inductor means of said explosive generator being connected in series in said electrical circuit;

d. a segmented inductive loop disposed in said electrical circuit and having a plurality of individual loop segments respectively connected in series in the electrical circuit with said explosive generator and in parallel with respect to each other;

e. means in said electrical circuit for discharging a pulsed electrical current through said inductor means of said explosive generator; and

f. said detonator means being actuatable in timed relation to the discharge of the pulsed electrical current through said inductor means to detonate the explosive contained in said armature for successively expanding said armature to cause progressive contact between said armature and said inductor means of the explosive generator along the lengths thereof for compressing magnetic flux, whereby the compressed magnetic flux is driven through said loop segments to establish a pulsed magnetic field within said segmented inductive loop. 

1. A high gain explosive generator system comprising: a. explosive generator means for establishing a pulsed electrical current; and b. inductive load means connected to said generator means, said load means comprising a single inductor member divided into physically separated segments, each of said segments being connected in electrical series with said generator means but in electrical parallel with each other.
 2. A high gain explosive generator system comprising: a. explosive generator means for establishing a pulsed electrical current; and b. inductive load means connected in series to said generator means, said load means comprising a single discontinuous inductive loop having a plurality of segments connected in electrical parallel with each other.
 2. inductor means surrounding said armature; and
 3. A method of simulating the electromagnetic effects of a nuclear detonation comprising: a. enclosing a volume with a discontinuous inductive loop having a plurality of segments connected in electrical parallel; and b. driving a pulsed electric current from an explosive generator through said loop segments to establish a pulsed magnetic field within the enclosed volume, each of said segments being connected in electrical series with the explosive generator.
 3. detonator means in proximity to the explosive contained in said armature and actuatable for detonating the explosive; c. said armature and said inductor means of said explosive generator being connected in series in said electrical circuit; d. a segmented inductive loop disposed in said electrical circuit and having a plurality of individual loop segments respectively connected in series in the electrical circuit with said explosive generator and in parallel with respect to each other; e. means in said electrical circuit for discharging a pulsed electrical current through said inductor means of said explosive generator; and f. said detonator means being actuatable in timed relation to the discharge of the pulsed electrical current through said inductor means to detonate the explosive contained in said armature for successively expanding said armature to cause progressive contact between said armature and said inductor means of the explosive generator along the lengths thereof for compressing magnetic flux, whereby the compressed magnetic flux is driven through said loop segments to establish a pulsed magnetic field within said segmented inductive loop.
 4. A method of creating a pulsed magnetic field in a confined volume comprising: a. discharging a pulsed electrical current through the inductor of an explosIve generator comprising an explosive-containing armature and an inductor surrounding the armature; b. detonating the explosive contained in the armature of the explosive generator in timed relation to the discharge of the pulsed electrical current through the inductor of the explosive generator such that successive expansion of the armature due to the detonation of the explosive contained therein causes progressive contact between the armature and the inductor of the explosive generator along the lengths thereof for compressing magnetic flux; and c. directing the compressed magnetic flux having a substantial increase in current and energy from the pulsed electrical current through a segmented inductive loop having a plurality of individual loop segments respectively connected in series in an electrical circuit with the explosive generator and in parallel with respect to each other.
 5. A high gain explosive generator system comprising: a. an electrical circuit; b. explosive generator means disposed in said electrical circuit for providing compressed magnetic flux upon actuation thereof by an explosion; c. a segmented inductive loop disposed in said electrical circuit and having a plurality of individual loop segments respectively connected in series in the electrical circuit with said explosive generator means and in parallel with respect to each other; d. means in said electrical circuit for discharging a pulsed electrical current through at least a portion of said explosive generator means; and e. means operating in timed relation to the discharge of the pulsed electrical current to cause an explosion actuating said explosive generator means, whereby the compressed magnetic flux provided by the actuation of said explosive generator means is driven through said loop segments to establish a pulsed magnetic field within said segmented inductive loop.
 6. A high gain explosive generator system comprising: a. an electrical circuit; b. an explosive generator disposed in said electrical circuit and comprising; 